Corrosion inhibiting cap for electrical terminals

ABSTRACT

A cap for protecting an electrical terminal from corrosion having a base which is insertable upon the terminal, a tapered section designed to guide and surround a mate to the terminal as it is being connected, and a removable top which protects the terminal before connection. The tapered section deforms during the connection operation to surround the mating terminal and seal the connection from corroding species.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a cap which fits over one electrical terminaland which seals itself to a mating electrical terminal to inhibitcorrosion.

2. Description of Related Art

The concept of an information highway is now developing into hardwarewhich will provide wide bandwidth service to every home and office inthe telephone loop plant. The location of this hardware placesenvironmental burdens upon network interface units, particularly withrespect to corrosion and its effect upon error free operation. Theseunits, which interconnect the loop plant to interior circuitry mustwithstand wide temperature excursions and the effects of contaminationand moisture. The contaminating species may be air-borne, such ascorrosive gases, or they may be particulate contamination, which maybecome dissolved in water from rain or condensation. Temperatureexcursions which permit early morning condensation have been found to beparticularly offensive because the amount of water is small and theconcentration of contaminants is high. Dissolution of some of thecontaminate material then forms an acid which corrodes electricalterminals.

Reducing cost is another factor to ensure the universal acceptance ofwide-bandwidth systems, so inexpensive connectors have been developedwhich are intended for indoor use. These are commonly known as “F-type”connectors, and because of their low cost and wide availability; theyhave also been used in external applications, with unreliable results.

Attempts have been made to protect these connectors by covering themwith a cap to exclude the environment, particularly during shipment andinstallation. The caps are removed upon installation, but corrosivegases and ionic contamination still seep through the threads of theF-type connector and corrode the center conductor. This corrosion layerincreases the resistance of the conduction path and causes interferencein video or data signals.

Accordingly, there is an increased need in the art for an inexpensiveconnector which provides reliable, error-free operation over a range ofenvironmental conditions which are to be encountered in the loop plantor any corrosive environment. It would be particularly desirable to usethe same inexpensive connector in both interior and exteriorapplications to minimize cost and inventory. Further, it is desirable tocontinue using a connector which is already in widespread use byprotecting it with an inexpensive cap which will provide corrosionprotection before installation and during extended use. In addition,there is a need to minimize the amount of material which is discardedwhen the connector is mated.

SUMMARY OF THE INVENTION

The present invention relates to an electrical terminal which isprotected from corrosive environments by a cap which seals elementswhich are sensitive to corrosion from gases or electrolytes.

In one embodiment of the invention, a base, tapered section, and topdefine a volume which is open at the base end. The inner dimension ofthe base is slightly smaller than the terminal it is intended to protectfrom corrosion. The base is forced part-way onto this terminal therebycreating an interference fit and seal. When the terminal is to beconnected to its mate, the top is removed leaving the tapered sectionand base attached to the terminal. The mate is guided by the taperedsection and forced into the base to create another interference fit andseal. The base, tapered section, and top are made from a polymer,typically polyethylene, and preferably a corrosion intercept reactivepolymer. A scored section may be added between the tapered section andthe top to ensure separation at that section. An extension section mayalso be added adjacent to the top to provide more space for the terminalduring storage and shipment. The terminal and its mate may provideconnection to a battery, an electronic circuit, or a radio frequencycircuit. The terminal may be any shape, but more frequently it isrectangular or circular, and it may comprise single or multiple pins.

In another embodiment of the invention, one portion of a connector,either a plug or a receptacle, is capped with the apparatus describedabove, and they are provided together as an assembly. On installation,the top is removed and the mate is forced into the body to make theconnection and create the seal against corrosion.

In still another embodiment of the invention, a polymer cap comprisingan annular base, a tapered section, an extended section, and a topdefine a volume which is open at the base. The base of the cap isadapted to deform around the plug and receptacle of a radio frequencyconnector.

With this cap, the same inexpensive radio frequency connectors arecapable of both indoor and outdoor use, minimizing cost and inventory.The cap provides corrosion protection to the connector in both the matedand unmated condition. The amount of discarded material is also limitedto the top of the cap.

These and other features and advantages of the invention will be betterunderstood with consideration of the following detailed description ofthe preferred embodiments taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of one embodiment of the invention;

FIG. 2 is a cross sectional view of another embodiment of the invention;

FIG. 3 is a cross sectional view of still another embodiment of theinvention; and

FIG. 4 is a cross sectional view of a mated connector pair protected bythe invention.

The drawings are not to scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The distribution of wideband communications facilities to provideuniversal service to homes and offices in the telephone loop plant maybe accomplished with coaxial or other cables which terminate in anetwork interface unit. Hardware exists which meets militaryspecifications to resist environmental conditions, but to promoteuniversal service and meet competition, this hardware must also beprovided at relatively low cost while ensuring error-free operation.This invention is not limited to connectors adapted to radio frequencyoperation, because there is also a need to protect terminals inapparatus such as batteries from the effects of corrosion.

Referring now to FIG. 1, there is shown apparatus 5 which is oneembodiment of the invention wherein a polymer base has a sidewall 12, afirst end 13, and a second end 14. The second end of the base supports atapered section having a sidewall 20, a first end 21, and a second end22. The second end of the tapered section supports top 30. The innerdimension of the base is selected to provide an interference fit arounda terminal (not shown) which is to be protected from corrodant species,either gaseous or in dissolved ionic form. In the discussion whichfollows, the terminal may be rectangular or circular, it may be a singlepost or it may comprise a multiplicity of pins, it may be a plug or areceptacle, and it may be designed to transmit any signal from DC toradio frequency or microwave frequency. The terminal could therefore bea post of a battery, the connector to an electronic circuit, or acoaxial type connector to a microwave circuit. Typically, the base is anannulus, the tapered section is the frustum of a cone, and the top iscircular. The base, tapered section, and the top define a volume whichis open at the first end 13 of the base. The base may be selected fromthe class of any thermoset or thermoplastic materials. An example ispolyethylene, and a preferred embodiment is a corrosion interceptreactive polymer. This material is described in U.S. Pat. No. 4,944,916given to Franey, Jul. 31, 1990, the description of which is incorporatedherein. The advantageous property of a corrosion intercept reactivepolymer is that it neutralizes corrosive gases by chemical reactionbetween a sacrificial material in the polymer matrix and corrosive gasessuch as sulfur or chlorine based compounds. Accelerated tests have shownthat a connector which would otherwise be corroded has an expected lifeof 20 years when protected by the cap.

To protect the terminal before installation and in shipment, apparatus 5is pushed on to the terminal by placing first end 13 over the terminal.A force is required to slightly expand the inner dimension of the baseand to slide it over the terminal. The thickness of sidewall 12 mayrange from 30 to 100 mils. The dimensions are selected to provide asecure interference fit over a particular terminal thereby protecting itfrom corrosive species. Apparatus 5 is forced on to the terminal untilabout half of the sidewall is in contact with the terminal. When aconnection is to be made to the terminal, top 30 is torn away fromsecond end 22 of the tapered section. The thickness of sidewall 20 ofthe tapered section is selected so that the break occurs at second end22, and the thickness may range from 10 to 40 mils, with a 25 milthickness being typical. The thickness of the top may range from 50 to100 mils. The mate to the terminal is then guided by the tapered sectiontoward the base and forced into that portion of the base which is not incontact with the terminal. The mate also makes an interference fit withthe base so that the base surrounds both the terminal and its mate andseals their connection from corroding species. A typical interferencebetween the base and the side of the terminal being 5 to 10 mils for a250 mil diameter terminal.

Referring now to FIG. 2, there is shown apparatus 6 in accordance withanother embodiment of the invention comprising a base and top sectionwhose elements numbered from 12 to 22 have been described above and areincorporated here. Second end 22 of the tapered section terminates atscored section 40. In this section the thickness of the sidewall isreduced by 30% to 70% to ensure that separation of the tapered sectionfrom first end 51 of extension section 50 occurs at the scored section.Second end of the extension section supports top 30. The operation andmaterials of apparatus 6 is similar to that of apparatus 5. About halfof the base is forced over the terminal and the mate is guided by thetapered section toward second end 14 of the base and forced down intothe base in an interference fit.

Referring now to FIG. 3, there is shown capped connector assembly 7comprising a cap whose elements numbered 12 through 52 have beendescribed in the description of apparatus 6 and are incorporated here.Sidewall 12 of the base surrounds plug 60 which is shown as onecomponent of a connector, in this figure it is shown as a coaxialconnector, and the component protected by the cap may be either a plugor a receptacle. Element 60 could also be the terminal of a battery or amultipin connector leading to an electronic circuit. The cap is insertedover plug/receptacle 60 so that portion 15 of sidewall 12 does notcontact plug/receptacle 60. When the connection is to be made, top 30and extension section 50 are removed from tapered section 20 at scoredsection 40. The mate (91 in FIG. 4) to plug/receptacle 60 is then guidedtoward second end 14 by the tapered section and it is forced into thebase so that portion 15 is expanded to fit around the mate, seal theconnection, and protect it from corroding species.

Referring now to FIG. 4 there is shown by way of example a mated coaxialconnector pair comprising plug 90 which is screwed into receptacle 91.Surrounding both of these elements is body 12 which is expanded slightlyto create an interference fit between itself and both the plug andreceptacle. Corroding species, whether gaseous or ionic, are therebyprevented from reaching and attacking the center conductor and threadedportions of the connector.

The advantages of this structure are that inexpensive connectors whichare already in wide use for indoor applications may be applied tooutdoor hardware minimizing cost, inventory, and the amount of materialdiscarded.

Changes and modifications in the specifically described embodiments canbe carried out without departing from the scope of the invention. Inparticular, a plug may be used for a receptacle, and vice versa, aterminal may refer to a single pin terminal or to a multipin terminal,and all the aforementioned connectors may be designed to operate fromdirect current to microwave frequencies. In addition, the cap may beused to protect non-electrical connections such as bolts which are usedin mechanical or-civil engineering applications.

I claim:
 1. An apparatus for protecting a terminal, said apparatuscomprising a housing including a base and a top, said base and topdefining a volume sufficient to surround said terminal when saidapparatus is disposed on said terminal, said base and top beingconfigured to be separable from one another so as to form a remainingportion and a disposable portion upon separation, said housing beingexpandable so as to form a seal that protects said terminal fromcorrosion in at least one of a mated condition and an unmated condition,said mated condition being one wherein said terminal is connected to amating member and said unmated condition being one wherein said terminalis not connected to said mating member.
 2. The apparatus of claim 1,wherein said seal protects said terminal from corrosion in said unmatedcondition.
 3. The apparatus of claim 2, wherein said seal protects saidterminal from corrosion in said mated condition when said disposableportion has been separated from said remaining portion.
 4. The apparatusof claim 1, wherein said seal protects said terminal from corrosion insaid mated condition.
 5. The apparatus of claim 4, wherein saidconnecting of said terminal to said mating member forms a connectionthat said remaining portion protects from corrosion.
 6. The apparatus ofclaim 1, wherein said remaining portion extends beyond an end of saidterminal.
 7. The apparatus of claim 1, wherein said remaining portionforms a lateral seal around an endmost portion of said terminal whensaid terminal is in said unmated condition.
 8. The apparatus of claim 7,wherein said remaining portion protects said terminal from corrosion insaid mated condition.
 9. The apparatus of claim 1, wherein, uponapplication of said apparatus to said terminal, said top and baseprotect said terminal from corrosion in said unmated condition.
 10. Theapparatus of claim 1, wherein said base and top are separable from oneanother at a predetermined location so as to form said remaining portionand said disposable portion upon separation.
 11. The apparatus of claim10, wherein said top includes a lip to facilitate said separation. 12.The apparatus of claim 11, wherein said housing includes an extensionsection interposed between said lip and said predetermined location. 13.The apparatus of claim 1, wherein said base has an inner dimensionsmaller than an outer dimension of said mating member, said expansionresolving the difference between said inner dimension and said outerdimension of said mating member.
 14. The apparatus of claim 13, whereinsaid base has an inner dimension smaller than an outer dimension of saidterminal, said expansion resolving the difference between said innerdimension and said outer dimension of said terminal.
 15. The apparatusof claim 1, wherein said base is made from a corrosion interceptreactive polymer.
 16. The apparatus of claim 1, wherein said housingdoes not comprise heat-shrinkable material.
 17. A method for protectinga terminal, said method comprising the steps of: providing a housingthat includes a base and a top, said base and top defining a volumesufficient to surround said terminal, said base and top being configuredto be separable from one another so as to form a remaining portion and adisposable portion upon separation; and expanding said housing so as toform a seal to protect said terminal from corrosion in at least one of amated condition and an unmated condition, said mated condition being onewherein said terminal is connected to a mating member and said unmatedcondition being one wherein said terminal is not connected to saidmating member.
 18. The method of claim 17, further comprising the stepof: separating said base and top from one another to form said remainingportion and said disposable portion.
 19. The method of claim 17, whereinsaid expansion step forms a seal that protects said terminal by forminga seal in both said mated condition and said unmated condition.
 20. Themethod of claim 19, further comprising the step of: separating said baseand top from one another to form said remaining portion and saiddisposable portion.
 21. The method of claim 20 wherein said separatingstep is performed after said step of expanding said housing so as toprotect said terminal from corrosion in said unmated condition.
 22. Themethod of claim 21, wherein said expanding for an unmated conditionforms a lateral seal around an endmost portion of said terminal.
 23. Themethod of claim 22, wherein said separating step is performed beforesaid step of expanding said housing so as to protect said terminal fromcorrosion in said mated condition.
 24. The method of claim 19, whereinsaid base has an inner dimension smaller than an outer dimension of saidmating member and an inner dimension smaller than an outer dimension ofsaid terminal; said seal-forming in said expanding step for said unmatedcondition occurs by resolving the difference between said innerdimension of said base and said outer dimension of said terminal; andsaid seal-forming in said expanding step for said mated condition occursby resolving the difference between said inner dimension of said baseand said outer dimension of said mating member.